Abstract: A technique for use in communications systems utilizing busy and idle modes. In the busy mode, symbols representative of data are transmitted to system end users. In the idle mode, during which no data is communicated to end users, idle mode symbols are transmitted. Such idle mode symbols are not used to represent data and are only transmitted during the idle mode. Advantageously, such idle mode symbols maintain adaptive apparatus, such as AGC circuits, NEXT cancellers and equalizers, in their properly converged state. In the disclosed embodiment, the idle mode symbols are the innermost symbols in a signal constellation and transition from the idle to busy mode is represented by the transmission of a predetermined number of outermost symbols in the signal constellation. Use of such symbols for idle-to-busy mode transitions advantageously provides ready detection of such transitions. In addition, use of the innermost symbols for the idle mode reduces spectral emission and crosstalk.

Abstract: An error-free, data telecommunication system designed for continuous high speed error-free data communications over dial-up voice grade circuits comprising a high speed data transmission section including internal data buffering and a low speed reverse channel ARQ (automatic request for repeat) receiver and a high speed data receiving section including a low speed reverse channel ARQ transmitter whereby high speed data and reverse ARQ signaling are transmitted simultaneously over a two wire dial-up network. The system is capable of half-duplex, two wire operation and full-duplex, four wire operation.